1. Field of the Invention
The present invention relates to a multiple-band mobile transceiver which operates for a plurality of mobile communications systems using different radio frequency bands by switching between transmission and reception radio frequencies.
2. Description of the Related Art
FIG. 3 shows the configuration of a conceivable mobile transceiver which operates for a plurality of mobile communications systems using different radio frequency bands. Reference numeral 1 denotes an antenna; 2 and 3, duplexers corresponding to two respective radio frequency bands; 4 and 5, isolators corresponding to two respective transmission frequency bands; 6 and 7, power amplifiers corresponding to the respective transmission frequency bands; 8, a high-frequency switch; 9, a variable gain amplifier; 10, a transmission mixer; 11, a lowpass filter; 12, a variable gain amplifier; 13, a quadrature modulator; 14 and 15, lowpass filters for I and Q modulation input signals; 16 and 17, I and Q modulation input terminals; and 18, a first local oscillator. Further, reference numerals 19 and 20 denote low-noise amplifiers corresponding to two respective reception frequency bands; 21 and 22, reception mixers corresponding to the respective reception frequency bands; 23 and 24, intermediate frequency filters corresponding to two respective reception intermediate frequencies; 25, an intermediate frequency switch; 26, a variable gain amplifier; 27, a quadrature demodulator; 28 and 29, lowpass filters for I and Q demodulation outputs; 30 and 31, I and Q demodulation output terminals; 34, a local oscillator for transmission modulation; and 35, a second local oscillator for reception.
Signals that are input from the I and Q modulation input terminals 16 and 17 are modulated by the quadrature modulator 13, and then up-converted into a radio frequency by the transmission mixer 10. A resulting signal is subjected to a gain adjustment by the variable gain amplifier 9, and then input to the power amplifiers 6 or 7 selected by the high-frequency switch 8 for the transmission frequency band concerned. An output of the power amplifier 6 or 7 is passed through the isolator 4 or 5, and then input to the duplexer 2 or 3 corresponding to the radio frequency band concerned. Finally, the signal is transmitted from an antenna 1 to a radio base station as radio waves.
On the other hand, a signal transmitted from a radio base station is separated from transmission waves of the mobile transceiver by the duplexer 2 or 3 corresponding to the radio frequency band concerned, amplified by the low-noise amplifier 19 or 20 corresponding to the reception frequency band concerned, and then converted into a signal of the reception intermediate frequency concerned by the reception mixer 21 or 22. An output of the reception mixer 21 or 22 is passed through the intermediate frequency filters 23 or 24 corresponding to the reception intermediate frequency concerned, and then selected by the intermediate frequency switch 25. An output of the intermediate frequency switch 25 is subjected to a gain adjustment by the variable gain amplifier 26, and then converted into I and Q demodulation signals by the quadrature demodulator 27.
However, in the above-configured mobile transceiver, the local oscillator for transmission modulation and the second local oscillator for reception need to be provided as separate frequency synthesizers. This is disadvantageous in terms of the cost and the number of parts.
It is noted that a mobile transceiver is known in which the duplexer 3, isolator 5, power amplifier 7, high-frequency switch 8, low-noise amplifier 20, reception mixer 22, intermediate frequency filter 24, and intermediate frequency switch 25 are omitted from the multiple-band mobile transceiver of FIG. 3.